From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id BBF35C433FE for ; Sun, 2 Oct 2022 23:51:13 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229453AbiJBXvL (ORCPT ); Sun, 2 Oct 2022 19:51:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:47150 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229441AbiJBXvI (ORCPT ); Sun, 2 Oct 2022 19:51:08 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id C323A3473E; Sun, 2 Oct 2022 16:51:05 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id CC4D460EE8; Sun, 2 Oct 2022 23:51:04 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 2AE6EC433C1; Sun, 2 Oct 2022 23:51:04 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1664754664; bh=8i2j1Equju5bv3X+GNDN7PBDR6BJY7fFXuyecJ1ahQU=; h=Date:From:To:Cc:Subject:Reply-To:References:In-Reply-To:From; b=hqigFUVTeufPfPy+iTvB+26TQjkCMQ850diAR0GpPs3C023RACXOZdBSFYIYh/4gN vwMAp6MwsVcHynpp2KPOwKpKYBaA/ukOfsTGOEWs1XIcVllcS/t2qJFfsHI6G1wCwe 7I5lqmNjNppynIN12ljwixh7mY+cyEGg67gvEmdjQXjIoluQB5jiMv8OaK8cPG1n7s jVcKZezTz9/zyHdnkC44ZorprFwYs/s9Y64zOn+Ka9F9rOvLoWz4V0QWpBzUNzq5Ex O6fFYBPA0xjF9Fiuhg3QhDdOUEkIKu9y63z/+ivhfnALpNqSybckPyypR4OujUb435 VxhUZSM48AaXQ== Received: by paulmck-ThinkPad-P17-Gen-1.home (Postfix, from userid 1000) id BFE005C0BE3; Sun, 2 Oct 2022 16:51:03 -0700 (PDT) Date: Sun, 2 Oct 2022 16:51:03 -0700 From: "Paul E. McKenney" To: Frederic Weisbecker Cc: rcu@vger.kernel.org, linux-kernel@vger.kernel.org, kernel-team@fb.com, rostedt@goodmis.org, Thomas Gleixner , John Ogness , Petr Mladek Subject: Re: [PATCH RFC v2 rcu 3/8] srcu: Check for consistent per-CPU per-srcu_struct NMI safety Message-ID: <20221002235103.GW4196@paulmck-ThinkPad-P17-Gen-1> Reply-To: paulmck@kernel.org References: <20220929180714.GA2874192@paulmck-ThinkPad-P17-Gen-1> <20220929180731.2875722-3-paulmck@kernel.org> <20221002220619.GA298433@lothringen> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20221002220619.GA298433@lothringen> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Mon, Oct 03, 2022 at 12:06:19AM +0200, Frederic Weisbecker wrote: > On Thu, Sep 29, 2022 at 11:07:26AM -0700, Paul E. McKenney wrote: > > This commit adds runtime checks to verify that a given srcu_struct uses > > consistent NMI-safe (or not) read-side primitives on a per-CPU basis. > > > > Link: https://lore.kernel.org/all/20220910221947.171557773@linutronix.de/ > > > > Signed-off-by: Paul E. McKenney > > Cc: Thomas Gleixner > > Cc: John Ogness > > Cc: Petr Mladek > > --- > > include/linux/srcu.h | 4 ++-- > > include/linux/srcutiny.h | 4 ++-- > > include/linux/srcutree.h | 9 +++++++-- > > kernel/rcu/srcutree.c | 38 ++++++++++++++++++++++++++++++++------ > > 4 files changed, 43 insertions(+), 12 deletions(-) > > > > diff --git a/include/linux/srcu.h b/include/linux/srcu.h > > index 2cc8321c0c86..565f60d57484 100644 > > --- a/include/linux/srcu.h > > +++ b/include/linux/srcu.h > > @@ -180,7 +180,7 @@ static inline int srcu_read_lock_nmisafe(struct srcu_struct *ssp) __acquires(ssp > > int retval; > > > > if (IS_ENABLED(CONFIG_NEED_SRCU_NMI_SAFE)) > > - retval = __srcu_read_lock_nmisafe(ssp); > > + retval = __srcu_read_lock_nmisafe(ssp, true); > > else > > retval = __srcu_read_lock(ssp); > > Shouldn't it be checked also when CONFIG_NEED_SRCU_NMI_SAFE=n ? You are asking why there is no "true" argument to __srcu_read_lock()? That is because it checks unconditionally. OK, so why the "true" argument to __srcu_read_lock_nmisafe(), you ask? Because srcu_gp_start_if_needed() needs to call __srcu_read_lock_nmisafe() while suppressing the checking, which it does by passing in "false". In turn because srcu_gp_start_if_needed() cannot always tell whether its srcu_struct is or is not NMI-safe. Thanx, Paul